The arrest of separatist Kashmiri leader Ghulam Nabi Fai on charges of working for the ISI could very well add to the already tensed atmosphere between the US and Pakistan, a media report has said.

The arrest of separatist Kashmiri leader Ghulam Nabi Fai on charges of working for the ISI could very well add to the already tensed atmosphere between the US and Pakistan, a media report has said.

"In a move that could add to the tension between the United States and Pakistan, the FBI on Tuesday accused a Pakistani-American of secretly funneling at least $ 4 million from Pakistan's top spy agency into American political activities, aiming to influence US policy on Kashmir," reported ProPublica; the popular investigative news website.

Fai, 62, ran the Washington-based Kashmiri American Council (KAC) which the FBI alleged lobbied at the Congress and the Administration on behalf of Pakistan without declaring himself as the a Pakistani agent.

"It's not clear where all the money went—much seemed to go to setting up conferences — but some was funneled into campaign contributions to members of Congress and other political candidates. The supporting affidavit says the money has been coming in from Pakistan's Inter-Services Intelligence Directorate, or ISI, since 1995," ProPublica said.

The charges could be the first implicating Pakistan's main intelligence service in a case involving political influence by foreign agents, a US law enforcement official told ProPublica.

"This charge is extremely rare," the official, who spoke on condition of anonymity, told the website.

"They don't happen very often. The government generally works to get someone into compliance rather than charging. I am not aware of any other cases that have involved Pakistan," the official said.

"Mr Fai is accused of a decades-long scheme with one purpose—to hide Pakistan's involvement behind his efforts to influence the US government's position on Kashmir," said US Attorney Neil MacBride of the Eastern District of Virginia.

The case is striking not necessarily for its severity— the charges against Fai and Ahmad would mean a maximum of only five years in prison — but for its depth, it said.

The FBI investigation appears to have started six years ago, when a jail inmate offered to trade information for a reduced jail sentence.

More than anything, the case highlights how, after years of US officials publicly treating the ISI like a close ally in the war on terror, their relationship has fallen apart, the report said.

ProPublica, who carried out several investigative report on the David Headley case, said the Fai case is in contrast to that.

According to ProPublica, Department of Justice has denied any motive behind the timing of the case and Fai's arrest.

"The timing had nothing to do with anything but the facts of the case," said Justice Department spokesman Dean Boyd.

"This is a long-term investigation and it predates recent developments in Pakistan and in relations with Pakistan. It was solely driven by the facts of the case," Boyd was quoted as saying by ProPublica.